This invention relates to ultrasonic inspection and, more particularly, to ultrasonic resonance spectroscopy for detecting crack-like defects.
Sound waves, i.e. ultrasonics, are used to perform a variety of nondestructive measurements for quality control in manufacturing processes and in detecting flaws and component characteristic changes arising from use of a component. One well known process uses echoes to locate crack-like defects at or below surfaces, as well as internal cavities and flaws. Such processes require sensitive equipment for echo detection and experienced operators to interpret the echo results.
Yet another ultrasonic inspection technique uses ultrasonic resonance characteristics to provide information on features of a specimen. For example, U.S. Pat. No. 4,428,235, issued Jan. 31, 1984, teaches a method for flaw characterization by comparing an ultrasonic resonance spectrum determined experimentally with a pattern obtained from a specimen being investigated. Four characteristic parameters are analyzed, namely (1) maximum spectrum strength, (2) center frequency, (3) mean value of frequency spacing between maxima in a frequency spectrum, and (4) standard deviation of the frequency spacing. These characteristics are used to determine changes in attributes of the specimen being examined. However, this technique requires that baseline or other reference information be known.
U.S. Pat. No. 4,829,823, issued May 16, 1989, describes a defect detection system using ultrasonic resonances. A mathematical model is established using known resonance frequencies of one or more exemplary work pieces having acceptable known characteristics, e.g., the coefficients of elasticity, weight, localized defects, and the like. The resonance frequencies for subsequent work pieces are then measured around frequency locations corresponding to the resonance frequencies of the exemplary pieces. Using the mathematical model, the selected characteristics of the subsequent work piece can be calculated from shifts in the resonance frequencies and used as a measure of acceptance or rejection of the piece. Again, exemplary measurements are required in order to implement the ultrasonic inspection scheme.
The need for exemplary data is overcome by the present invention and crack detection is accomplished by ultrasonic resonance inspection of a completed work piece without the need for a known standard or "good" resonance pattern. Accordingly, it is an object of the present invention to provide ultrasonic flaw detection from resonance characteristics of a single object.
It is another object of the present invention to enable the detection of incipient flaws in a work piece without the need for comparative resonance spectrum data.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.